Overload safety device for a crane

ABSTRACT

An overload safety device for cranes, particularly for mobile cranes, includes a housing preferably mounted on a surface of the crane boom which is under compression when loaded. Within the housing a plurality of cam discs are mounted on a shaft with each cam disc representing a specific boom or crane support arrangement. Each cam disc has a plurality of peripheral segmental surfaces and each of these surfaces represents a different operating length of the boom, such as in a telescopic boom. The shaft supporting the cam discs can be rotated to locate the applicable segmental surface in position for operation. Another shaft is located within the housing laterally offset from the shaft for the cam discs and it supports swivel arms located, under permissible load conditions, laterally outwardly from the cam discs. Adjacent swivel arms are arranged in pairs with each pair supporting a combination light source-photocell assembly. An expansion rod dynamometer is fixed to the boom and a cable extends from the dynamometer to the shaft for the swivel arms for pivoting the swivel arms and moving them into the range of the cam discs as the load on the boom approaches overload conditions. When overload conditions are reached, the cam discs interrupt the path between the light source and photocell and cut off further boom movements. Moreover, a pendulum arrangement is associated with the cam discs to assure proper orientation of the device as the crane and boom are moved.

United States Patent [191 Eiler OVERLOAD SAFETY DEVICE FOR A CRANE [75] Inventor: Peter Eller, Dusseldorf-Benrath,

Germany [73] Assignee: Leo Got twald K.G.,

Dusseldorf-Holthausen, Germany [22] Filed: Feb. 14, 1972 [21] App]. No.: 225,865

Primary ExaminerRichard E. Aegerter Assistant ExaminerMerle F. Maffei Atlorney-Toren and McGeady [57] ABSTRACT An overload safety device for cranes, particularly for [451 Aug. 28, 1973 mobilecranes includes ahousing preferably mounted on a surface of the crane boom which is under compression when loaded. Within the housing a plurality of cam discs are mounted on a shaft with each cam disc representing a specific boom or crane support arrangement. Each cam disc has a plurality of peripheral segmental surfaces and each of these surfaces represents a different operating length of the boom, such as in a telescopic boom. The shafi supporting the cam discs can be rotated to locate the applicable segmental surface in position for operation. Another shaft is located within the housing laterally offset from the shaft for the cam discs and it supports swivel arms located, under permissible load conditions, laterally outwardly from the cam discs. Adjacent swivel arms are arranged in pairs with each pair supporting a combination light source-photocell assembly. An expansion rod dynamometer is fixed to the boom and a cable extends from the dynamometer tothe shaft for the swivel arms for pivoting the swivel arms and moving them into the range of the cam discs as the load on the boom approaches overload conditions. When overload conditions are reached, the cam discs interrupt the path between the light source and photocell and cut off further boom movements. Moreover, a pendulum arrangement is associated with the cam discs to assure proper orientation of the device as the crane and boom are moved.

19 Claims, 3 Drawing Figures Patented Aug. 28, 1973 3 Sheets-Sheet 1 Patent ed Aug. 28, 1973 5 Sheets-Sheet 5 BMMW /w H OVERLOAD SAFETY DEVICE FOR A CRANE SUMMARY OF THE INVENTION The present invention is directed to an overload safety device for cranes, particularly for mobile cranes, and, more specifically, it concerns a mechanical arrangement for determining the existence of overload conditions on the crane.

Practical requirements for crane operation, as well as legal regulations, have necessitated the use of overload safety devices on mobile cranes to avoid accidents resulting from overload and several such safety devices are already known. In particular, the function of the safety device is to insure the stability of mobile cranes and in cranes with a movable boom the permissible load for the boom is limited by the stability of the crane. Therefore, cranes may be loaded, for safety reasons, to a limit which is below the maximum utilization based on the stability of the crane. At the present time, the known warning or shut-off safety devices have as a common feature electronic systems which consist of transmitters of forces and moments acting on the boom and as transmitters for geometric quantities, that is the boom angle, boom length and the like, and these systems work on the principle of comparing the nominal and actual value of two currents or voltages such as is used in automatic control technology. The actual values measured by the system are processed in a central unit and compared with nominal values stored in the unit. When the maximum permissible limit is reached, an automatic signal is transmitted and all crane operations which increase the load moments are ceased. It is the purpose of such systems to avoid burdening the crane operator with evaluating and comparing the data for forces and geometric quantities determined by the transmitters during a lifting or hoisting operation on the basis of tables and then making further crane or boom movements dependent on the result of such a comparison.

Though the operator is essentially free from working with tables and the like when using the presently known overload safety devices, these devices have considerable disadvantages due mainly to the fact that they are not adapted to operate under the conditions which exist in a mobile crane. Apart from the fact that highly sensitive electronic transmitters and plotters are very expensive and cannot withstand the rugged working conditions of a mobile crane, particularly with'regard to their life expectancy, any repairs required, if it is possible to perform them, involve considerable expenditure of time and money and, further, the device requires the attention of trained experts who normally are not available at the site of the crane.

Therefore, it is the primary object of the present invention to provide an overload safety device for a crane, particularly of the mobile type, which has low manufacturing costs and low susceptability to operating problems'and, in addition, in use it does not require any special operating experience. Accordingly, it is possible to avoid the use of electronic systems and, instead, to use mechanical equipment for transmitting the geometric conditions and forces to an element which blocks any load-increasing crane movements when a maximum limiting value of the load has been reached. Specifically, the invention utilizes the combination of at least one cam disc and swivel arm with the swivel arm having a combination light source-photocell assembly associated with it. A dynamometer is mounted on a loaded part of the crane boom and is mechanically connected to the swivel arm for pivoting into the range of the cam disc so that the path of light between the light source and the photocell is interrupted and the continuation of any overload conditions is avoided.

Based on the load conditions determined by the dynamometer, the swivel arm is pivoted and cooperates with the cam disc in cutting off crane operations at overload. The cam is shaped along its peripheral edge in accordance with predetermined, admissible parameters of the crane, for instance, the boom angle, the boom length, and the relative arrangement of the crane structure to its support. Accordingly, based on the conditions under which the crane is operating, the cam disc determines the point at which the path of light between the light source and the photocell is interrupted as the swivel arm pivots relative to the cam disc. Further, the combination light source-photocell assembly of the swivel arm, which is pivoted in dependence on the conditions measured by the dynamometer, is coupled electrically with a cut-off device for discontinuing crane movements which increase the load moment when the maximum permissible load condition has been reached. Preferably, the cut-off action is positively effected when the path of light between the light source and the photocell assembly or similar device is interrupted as the swivel arm pivots into the range of its associated cam disc.

A particularly space saving arrangement is provided by forming each cam disc with four contour segments each corresponding to a respective condition of the crane. Therefore, since all cranes have a maximum working range of a angle of traverse of the boom in the vertical direction, it is possible, with a single cam disc, to provide a surface which-determines each of the different crane conditions, that is with the boom projecting in the longitudinal and in the transverse directions of the crane support axis and with the crane arranged in the supported and unsupported condition.

To assure that the vertically suspended load is always taken into account as the primary value for the switching operation of the overload safety device and that the possibly tilted orientation of the crane does not cause any erroneous value, as occurs in presently known devices, a pendulum is frictionally coupled to the shaft on which the cam disc is mounted to assure proper orientation of the cam disc. Due'to the effect of gravity acting on the pendulum, the cam disc is properly oriented in accordance with the vertically suspended load, even if the crane is in a tilted position. For checking the operability of the pendulum, a control pendulum is associated with it and is mounted on an axis offset from the axis of the shaft on which the pendulum is supported so that if the pendulum does not assume a vertical position, the non-aligned positions of the pendulum and the control pendulum will indicate this defect. Preferably, the aligned arrangement of the pendulums is provided by mounting a light source on one of them and a photocell on the other which are in alignment when the pendulums are operating properly and issue a warning signal if the pendulums should become misaligned.

To prevent the normally vigorous crane movement from resulting in a swinging action of the cam discs on their shaft, the free end of the pendulum mounted on the shaft is positioned within a fluid which affords a damping action on the movement of the shaft and cam discs as a result of any crane movements.

As indicated above, in the present invention the cam disc or discs afford the possibility of taking into account the various conditions of the crane in establishing the limiting values of the maximum permissible load on the crane. This feature requires that it must be possible to rotate the cam disc in the field or range of movement of the swivel arm with its combination light source-photocell assembly in correspondence with the particular position or arrangement of the crane, that is with its boom extending in the longitudinal direction or transversely of the axis of its support and with the crane in the supported or unsupported condition. The positioning of the cam discs is effected through a locking plate mounted on the cam disc shaft and the locking plate carries a locking pin which cooperates with a spring loaded setting member containing four angularly spaced recesses into which the locking pin can be secured. The setting member is fixed to the cam disc shaft and can be rotated by a separate drive assembly for selecting the desired position of the locking pin. Preferably, the drive assembly for the setting member utilizes a windshield wiper motor. Accordingly, with this arrangement it is possible to disengage the locking pin and to move the setting member and the cam disc shaft for establishing the desired position of the cam disc and the locking pin relative to the recesses in the setting member. Accordingly, the desired segmental surface of the cam disc, based on the orientation of the crane, can be positioned for cooperation with its associated swivel arm. Further, as the segmental surfaces of the cam are rotated into position, the cam disc is coupled through the shaft with the pendulum. Further, the positioning of the segmental surfaces of the cam disc can also be effected manually, in which the case the pendulum is moved into an unlocked position against the action of a spring and, after the cam disc has been properly repositioned, the pendulum can be returned to its locked position.

While the invention has been described with regard to the use of a single cam disc, the range of use of the overload safety device can be increased if a plurality of axially spaced cam discs are arranged in parallel relationship to one another on the same shaft. When multiple cam discs are used, a swivel arm is associated with each cam disc and the adjacent swivel arms on the opposite sides of the cam disc provide the combination light source-photocell assembly. With multiple cam discs being used, each cam disc corresponds to a certain boom length and in the case of cranes with telescopic booms, a corresponding number of boom lengths can be selected corresponding to the load ranges established in the operating tables for determining the carrying capacities of the boom. Therefore, in cranes using telescopic booms, one cam disc is assigned to each longitudinal range of the boom based on the extendable arrangement of the boom.

To assure that proper interruption of the light path in a combination light source-photocell assembly is provided where multiple cam discs are being used, a pair of swivel arms are provided one on each side of the cam disc with one swivel arm supporting the photocell and the other supporting the light source. To afford a more efficient apparatus, an alternating arrangement of swivel arms can be provided with one swivel arm supporting two photocells and the adjacent swivel arms each supporting two light sources so that for each pair of adjacent swivel arms a combination light sourcephotocell assembly is provided.

Where multiple swivel arms are used, they are mounted on a common pivot which is coupled to the dynamometer through a cable and pulley arrangement. The dynamometer is designed as an expansion rod dynamometer and as it follows the load conditions on the boom it transmits these conditions to the common pivot through the cable and pulley arrangement for pivotally displacing the swivel arms relative to the cam discs. A lever system is incorporated with the dynamometer so that a sufficiently long path is provided based on the movement experienced by the dynamometer for assuring adequate pivotal movements of the swivel arms.

Further, where multiple cam discs are being used, the switching operation can besimply effected by electrically connecting the combination light sourcephotocell assembly associated with the particular cam disc while the remaining assemblies are left in the off condition. As the load acting on the boom changes, the swivel arms pivot about their shaft and move toward the cam discs as the load increases. The positive discontinuance of the boom operation occurs only when the respective light source-photocell assembly moves into the range of the corresponding cam disc without any effect being caused by the relative relationship of the other swivel arms and their associated cam discs. In this way only a single operating condition of the boom is determined by the device.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a side elevational view of a portion of a crane boom and of an overload safety device embodying the present invention;

FIG. 2 is a sectional view taken along the line ll-ll in FIG. 1; and

FIG. 3 is a sectional view taken along the line IIIIll in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION In the drawing, an overload safety device 11 is secured to a crane boom I2, only a portion of which is shown in FIGS. 1 and 3, by means of a holder or bracket 13, note FIGS. 2 and 3. The overload safety device l 1 includes a housing 14 subdivided by a partition 17 into two compartments l8, 19. The partition 17 supports a shaft or pivot rod 15 and another shaft 16, the shaft 16 is rotatably mounted in the partition 17 and extends laterally from the partition into both of the compartments. Within the compartment 18 a plurality of cam discs 21 are arranged in axially spaced parallel relationship and the circumferential edges of the discs are shaped to correspond to the parameters of the craneand boom influencing the maximum permissible load and taking into account the boom angle alpha, note FIG. 1. As can be seen in FIG. 1, each cam disc is divided into quadrants or four segmental surfaces each corresponding to a particular condition of the crane, that is, in the case of a truck crane with the truck supported, with the truck unsupported, with the boom-extending transversely of the longitudinal axis of the truck and with the boom aligned parallel to the longitudinal axis of the truck. Further, each cam disc is arranged to correspond to a certain length of the boom and in the case of a telescopic crane boom each disc covers a certain longitudinal extension of the telescopic boom.

Within the compartment 19, a locking plate 22 is rotatably mounted on the shaft 16 and a locking pin 31 is secured to and extends outwardly from the locking plate in parallel relationship with the axis of the shaft and in a direction away from the partition 17. A pendulum 24 extends downwardly from the lower end of the locking plate and intermediate its ends it supports a photocell and a light source 25, respectively. As seen in FIG. 2, an axis 26 extends outwardly from the locking plate 22 above and in parallel relationship with the shaft 16 and on the extension of the pendulum 24. Suspended on the axis 26 is a correction or control pendulum 27 which has a part 28 of a light barrier corre- I sponding to and cooperating with the photocell and ingly, when the angular position of the boom is changed, followed by the displacement of the overload safety device due to its positive connection boom, the movement of the pendulums are damped. Spaced closely from the locking plate 22 and non-rotatably mounted on the shaft 16 is a spring-loaded setting member 32 having four radially extending recesses 23 disposed 90 degrees apart, note FIG. 1. As can be seen in FIG. 2, the locking pin 31 extends from the locking plate 22 into one of the recesses 23 inthe setting member 32. Spaced axially from the face containing the recesses 23, the setting member has a circumferential edge 34 which extends radially outwardly within a casing member 35. The casing member.35 is mounted non-rotatably on a shaft 37 and is displaceable in the axial direction of the shaft against the force of a spring extending aroundthe shaft 37. A wind-shield wiper motor 38 is secured on the housing 14 and the shaft 37 extends from the motor into the compartment 19. A cam member 39 is mounted within the compartment 19 encircling the shaft 37 and a pin in the shaft cooperates with the cam member for affording axial displacement of the casing member. As the windshield wiper motor 38 rotates the shaft 37, the pin 41 riding on the cam surface 39 displaces the casing member 35 to the left, as seen in FIG. 2, so that the setting member 32 is displaced axially to the left in FIG. 2 by the casing member 35 with the recess 23 being removed from the range of the locking pin 31.

As can be seen in FIGS. 2 and 3, the pivot rod pivotally supports a plurality of swivel arms 42 spaced axially from one another and offset relative to the positions of the cam discs 21 on the shaft 16. As indicated in FIG 1, the pivot rod 15 is laterally offset relative to the shaft 16 so that the swivel arms which are in alignment with one another, are arranged in the vertical position laterally outwardly from the peripheral surfaces of the cam discs 21, that is the swivel arms are outside of the projection of the surface of the cam discs. The manner in which the swivel arms 42 pivot about the shaft or pivot rod 15 is shown by the dashed lines in FIG. 1 indicating the swivel arms in the space between adjacent cam discs. A balancing weight 40 is arranged above the pivot rod 15 for affording a weightless swivel movement for the arms 42. At the free ends of the swivel arms 42, note FIGS. 1 and 2, light wave means are provided, the end swivel arm, most remote from the windshield wiper motor, supports a light source 43 at its free end and the next adjacent swivel arm has a pair of photocells 44 supported at its free end one facing toward the outermost swivel arm and the other facing inwardly toward the next adjacent swivel arm in the direction of the windshield wiper motor. Similarly, the next inner swivel arm from the one containing the photocells supports a pair of light sources 45, 46, one facing away from the windshield wiper motor and aligned with the photocell on the next outwardly located swivel arm while the light source 46 faces toward the windshield wiper motor and is aligned with a photocell 44 on the next adjacent swivel arm closer to the windshield wiper motor. Accordingly, each pair of adjacent swivel arms provides a combination light sourcephotocell assembly with the light source and photocell disposed in alignment. The pattern of the light sourcephotocell arrangement is repeated for all the swivel arms, that is the swivel arms alternate in supporting either light sources or photocells for reducing the lead wires to the light sources and photocells and to insure, at the same time, an operation free of incidental light influences. The necessary lead wires can also be reduced to a minimum by securing a bulb 47 on the pivot rod 15 from which cable photoconductors extend to light sources.

Further, as is shown in FIG. 1, additional light sources 43a, photocells 44a can be located on the free ends of the swivel arms adjacent the above-mentioned light sources and photocells and more closely located to the peripheral edges of the cam discs so that the additional light sources 43a, photocells 44a are intercepted by the surface of the cam discs and, as a result, serve as an early warning of the approaching overload conditions of the crane.

An expansion rod dynamometer 52 is secured to the lower surface of the boom 12, that is the surface which is in compression when a load is suspended from the boom. Extending between the dynamometer 52 and a pulley 48 non-rotatably attached to the pivot rod '15 is a pull cable 49 which extends around a guide pulley 51 intermediate the location of the pivot rod- 15 and'the dynamometer 52. Further, a lever 53 is secured to and extends laterally outwardly or upwardly from the pivot rod 15 and a tension spring 54 is attached to the end of the lever outwardly from the pivot rod for affording a restoring force to the pivot rod 15 swivel arm 42 arrangement opposite to the pulling action of the cable 49.

As shown in the drawing, the expansion rod' dynamometer 52 is installed in the prestressed state under an initial stress which corresponds to the permissible maximum load for the boom. Since the dynamometer is mounted on the part of the boom which is under compression when loaded, that is the compression cord of the boom, the given expansion of the expansion rod disappears when the maximum load is attained, whereby the dynamometer detaches itself with increasing load from its anchoring points 55, note FIG. 3, and thus remains undamaged, for example, in the event the overload safety device is intentionally disconnected.

Further, the dynamometer can also be prestressed to the pressure corresponding to the maximum load, and in such a case the dynamometer would be secured on the part of the crane which is under tension when the load is applied.

As illustrated in FIG. 3, the cable 49 is secured at its end opposite from-the pulley 48 to swivel lever 56 whose deflection at initial load produced by the initial stress, that is, in the unloaded condition of the boom, corresponds, for example, to the distance h. The lever is supported by a stationary pivot 57 and it is maintained by a tension spring 58 in bearing against a stop 61 which moves with the expansion rod 59 of the dynamometer.

In operation the overload safety device of the present invention operates as follows: when the boom 12 is brought into its operating position, such as shown in FIG. 1, the pendulum 24 ensures a vertical alignment of all cam discs 21 through the medium of the setting member 32 which is fixed to the shaft 16. The pendulum action compensates for any tilted position assumed by the crane. In the path of the pivotal movement or swing of the swivel arms 42 about the pivot rod 15, as indicated by the arcuate dot-dash lines in FIG. 1, is a contour segment of the corresponding cam disc 21 which represents the limiting load conditions for the particular orientation of the crane and boom. When the adjacent pair of swivel arms pass inwardly, that is toward the shaft 16, of the peripheral edge of the intervening cam disc, the path of light between the light source and photocell of the combination light sourcephotocell assembly of the pair of swivel arms signals that an overload condition has been reached.

As soon as the crane is loaded, the initial stress of the dynamometer 52 disappears and the expansion rod contracts and turns the swivel lever 56 over the stop in the direction of the expansion rod. Accordingly, the cable 49 is moved clockwise in the same direction and, in turn, effects a similar rotation on the part of the pulley 48. As a result, the swivel arms 42 move in the direction of the shaft 16. As soon as the additional light source-photocells 43a, 44a move into the range of the peripheral surfaces of the cam discs 21, the path of light between the two is interrupted and an early warning signal is transmitted. If the movement of the swivel arms continues inwardly toward the shaft 16 then an automatic cut-off of the load-increasing crane movements is effected as the path of light between the combination light source-photocell assembly is interrupted by the surface of the cam discs at their edges.

If the connection between the swivel arms and the dynamometer should be interrupted for some reason, for example, by a break in the cable 49, any possible harmful overloads on the crane, which could no longer be indicated due to the failure in the connection between the swivel arms and dynamometer, is avoided by the spring 54 which effects a returning action to the swivel arms through the pivot rod and displaces the free ends of the swivel arms into the range ofa safety pocket 62 which also interrupts the light path between the combination light source-photocell assembly for discontinuing any crane movements which would contribute to an overload condition. As mentioned above, each quandrant of each cam disc 21 represents a certain operating condition of the crane, while each cam disc is associated with a certain boom length or a certain longitudinal range of the boom. 1f the operating condition of the crane is changed, for example, if the boom moves from a position transverse to the longitudinal direction of its support into the longitudinal direction of its support, the overload safety device is reset in a simple manner in accordance with the new operating conditions as follows: by actuating the windshield wiper motor 38, the pin 41 is moved along the surface of the cam 39 and during one revolution of the shaft 37 through the medium of the casing member 35 it releases the setting member 32 from the locking pin 31, that is the recess 23 into which the locking pin had been secured is withdrawn from the locking pin. The locking pin is then engaged with the next recess spaced degrees from the previous one with which the locking pin was engaged and the shaft and the cam discs are, in turn, rotated through the same 90. Accordingly, the overload safety device is set for a different operating condition of the crane.

Similarly, the safety device is reset for a different boom length in a very simple manner. To provide this change, only the combination light source-photocell assigned to the cam disc corresponding to the new boom length is activated, that is, it is connected electrically with the cut-off device so that only a signal generated by that cam disc operates the overload device, though all of the swivel arms effect the pivotal movement transmitted to the pivot rod 15 from the dynamometer 52. Accordingly, only the connected light source-photocell assembly is effective in operating the device when the ends of the corresponding swivel arms pass inwardly on either side of the peripheral edge surface of the corresponding cam disc. It would also be possible to connect the respective light sources, however, the use of cable photoconductors suggested according to the present invention, which are fed from a central light source, has the advantage of greater reliability and of savings in electrical connections.

Therefore, in accordance with the above description, the overload safety device is characterized by a very simple design and great resistance to shock loads such as occur in the operation of cranes, accordingly, the device can be used for all hoisting gear and related apparatus which are limited in their load carrying capacities by different factors.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. An overload safety device for cranes, particularly for mobile cranes, with the device mounted on the crane boom, said device comprising support means, a dynamometer secured to the boom, at least one pivotally supported swivel arm mounted on said support' means, a combination light source-photocell assembly associated with said swivel arm, at least one cam disc mounted on said support means at a position spaced laterally from the point at which said swivel arm is pivotally supported, means interconnecting said dynamometer and said swivel arm for pivotally displacing said swivel arm toward said cam disc as the load on said boom increases so that said cam disc interrupts the passage of light between the light source and photocell in said assembly when the maximum permissible load on said crane is exceeded.

2. An overload safety device, as set forth in claim 1, wherein said device includes a cut-off switch, said swivel arm connected electrically to said cut-off switch for discontinuing all crane movements when the maximum permissible load is exceeded.

3. An overload safety device, as set forth in claim 1, wherein said support means comprises a first shaft, said cam disc rotatably mounted on said first shaft.

4. An overload safety device, as set forth in claim 1, wherein each said cam disc has a plurality of contour segments formed on its peripheral edge with each segment corresponding to a different characteristic of said crane relative to its support and arrangement of its boom.

5. An overload safety device, as set forth in claim 3, 3

wherein a pendulum is pivotally mounted on said first shaft in spaced relationship to said cam discs for maintaining the proper vertical orientation of said cam discs.

6. An overload safety device, as set forth in claim 5,

4 wherein a pivot pin is spaced from and in substantially parallel relationship with said first shaft, a control pendulum positioned adjacent said pendulum and pivotally mounted on said pivot pin.

7. An overload safety device, as set forth in claim 6, wherein a light source is positioned on one of said pendulum and control pendulum and a photocell is positioned on the other one of said pendulum and control pendulum with said light source and photocell disposed in alignment when said pendulum and control pendulum are oriented vertically.

8. An overload safety device, as set forth in claim 7, wherein said device includes a housing enclosing said pendulum and control pendulum, a body of liquid contained in the lower portion of said housing, said pendulum and control pendulum extending downwardly into said body of liquid so that the liquid effects a damping action on said pendulums.

9. An overload safety device, as set forth in claim 3, wherein a locking plate is mounted on said first shaft spaced axially from said discs, a locking pin positioned in said locking plate, a spring loaded setting member fixed to said shaft and spaced axially from and adjacent to said locking plate, said setting member having a plurality of radially extending recesses therein spaced angularly apart, a drive means associated with said setting member for axially displacing said setting member on said first shaft and for selectively engaging said locking pin in one of said recesses in said setting member.

10. An overload safety device, as set forth in claim 3, wherein a plurality of said cam discs are mounted on said first shaft in axially spaced parallel relationship, said support means includes a second shaft spaced laterally from and in substantially parallel relationship with said first shaft, a plurality of said swivel arms mounted on said second shaft in axial spaced relationship and offset relative to said cam discs so that said swivel arms can pivot between said cam discs from a position spaced laterally outwardly from the peripheral edges of said cam discs, and adjacent said swivel arms arranged in pairs with each said pair supporting one said combination light source-photocell assembly with said light source located on one of said pair and said photocell located on the other one of said pair.

11. An overload safety device, as set forth in claim 10, wherein an additional combination light sourcephotocell assembly is located on each said pair of adjacent swivel arms with said additional light source located on one of said pair of said swivel arms and said additional photocell located on the other one of said pair of said swivel arms, and said additional combination light source-photocell assembly located on said swivel arm so that the path of light between the light source and photocell of said additional combination light source-photocell assembly is interrupted first by the peripheral edge of said cam disc as said swivel arm pivots toward said cam disc.

12. An overload safety device, as set forth in claim 10, wherein a pulley is frictionally coupled to said second shaft, said dynamometer arranged as an expansion rod, a cable secured to said pulley at one end and to said dynamometer at the other end so that as said dynamometer is displaced by the application of load to said boom said second shaft is rotated by said pulley.

13. An overload safety device, as set forth in claim 12, wherein said dynamometer is prestressed to the maximum allowable load.

14. An overload safety device, as set forth in claim 13, wherein said dynamometer is mounted on the portion of said boom disposed in compression under load conditions.

15. An overload safety device, as set forth in claim 14, wherein said dynamometer extends in the longitudinal direction of said boom and is mounted on the compression surface of said boom.

16. An overload safety device, as set forth in claim 10, wherein means are arranged for rotatably biasing said second shaft for displacing said swivel arms laterally outwardly away from said cam discs, and means forming a safety pocket for receiving said combinationphotocell assembly for interrupting the passage of light between the light source and the photocells thereof and discontinuing loading operations on said crane.

17. An overload safety device, as set forth in claim 10, wherein a bulb is positioned on said second shaft and said light sources consist of cable conductors extending from said bulb.

18. An overload safety device, as set forth in claim 8, wherein said housing encloses said cam discs, said swivel arms and said pendulums, a partition dividing said housing into two compartments, one of said compartments containing said cam discs and swivel arms and the other one of said compartments containing said pendulums, and said partition supporting said first shaft for said cam discs.

19. An overload safety device, as set forth in claim 9, wherein said setting member having a radially extending circumferential edge spaced axially from the face of said setting member containing said recesses and located more remotely from said cam discs than the face containing said recesses, a third shaft in axial alignment with said first shaft, an engagement member secured on and axially displaceable along said third shaft and arranged to engage said circumferential edge of said setting member, said drive means secured to said engagement member for axially displacing said engagement member into engagement with the circumferential edge of said setting member for axially displacing said setting member and removing it from engagement with said locking pin. 

1. An overload safety device for cranes, particularly for mobile cranes, with the device mounted on the crane boom, said device comprising support means, a dynamometer secured to the boom, at least one pivotally supported swivel arm mounted on said support means, a combination light source-photocell assembly associated with said swivel arm, at least one cam disc mounted on said support means at a position spaced laterally from the point at which said swivel arm is pivotally supported, means interconnecting said dynamometer and said swivel arm for pivotally displacing said swivel arm toward said cam disc as the load on said boom increases so that said cam disc interrupts the passage of light between the light source and photocell in said assembly when the maximum permissible load on said crane is exceeded.
 2. An overload safety device, as set forth in claim 1, wherein said device includes a cut-off switch, said swivel arm connected electrically to said cut-off switch for discontinuing all crane movements when the maximum permissible load is exceeded.
 3. An overload safety device, as set forth in claim 1, wherein said support means comprises a first shaft, said cam disc rotatably mounted on said first shaft.
 4. An overload safety device, as set forth in claim 1, wherein each said cam disc has a plurality of contour segments formed on its peripheral edge with each segment corresponding to a different characteristic of said crane relative to its support and arrangement of its boom.
 5. An overload safety device, as set forth in claim 3, wherein a pendulum is pivotally mounted on said first shaft in spaced relationship to said cam discs for maintaining the proper vertical orientation of said cam discs.
 6. An overload safety device, as set forth in claim 5, wherein a pivot pin is spaced from and in substantially parallel relationship with said first shaft, a control pendulum positioned adjacent said pendulum and pivotally mounted on said pivot pin.
 7. An overload safety device, as set forth in claim 6, wherein a light source is positioned on one of said pendulum and control pendulum and a photocell is positioned on the other one of said pendulum and control pendulum with said light source and photocell disposed in alignment when said pendulum and control pendulum are oriented vertically.
 8. An overload safety device, as set forth in claim 7, wherein said device includes a housing enclosing said pendulum and control pendulum, a body of liquid contained in the lower portion of said housing, said pendulum and control pendulum extending downwardly into said body of liquid so that the liquid effects a damping action on said pendulums.
 9. An overload safety device, as set forth in claim 3, wherein a locking plate is mounted on said first shaft spaced axially from said discs, a locking pin positioned in saiD locking plate, a spring loaded setting member fixed to said shaft and spaced axially from and adjacent to said locking plate, said setting member having a plurality of radially extending recesses therein spaced angularly apart, a drive means associated with said setting member for axially displacing said setting member on said first shaft and for selectively engaging said locking pin in one of said recesses in said setting member.
 10. An overload safety device, as set forth in claim 3, wherein a plurality of said cam discs are mounted on said first shaft in axially spaced parallel relationship, said support means includes a second shaft spaced laterally from and in substantially parallel relationship with said first shaft, a plurality of said swivel arms mounted on said second shaft in axial spaced relationship and offset relative to said cam discs so that said swivel arms can pivot between said cam discs from a position spaced laterally outwardly from the peripheral edges of said cam discs, and adjacent said swivel arms arranged in pairs with each said pair supporting one said combination light source-photocell assembly with said light source located on one of said pair and said photocell located on the other one of said pair.
 11. An overload safety device, as set forth in claim 10, wherein an additional combination light source-photocell assembly is located on each said pair of adjacent swivel arms with said additional light source located on one of said pair of said swivel arms and said additional photocell located on the other one of said pair of said swivel arms, and said additional combination light source-photocell assembly located on said swivel arm so that the path of light between the light source and photocell of said additional combination light source-photocell assembly is interrupted first by the peripheral edge of said cam disc as said swivel arm pivots toward said cam disc.
 12. An overload safety device, as set forth in claim 10, wherein a pulley is frictionally coupled to said second shaft, said dynamometer arranged as an expansion rod, a cable secured to said pulley at one end and to said dynamometer at the other end so that as said dynamometer is displaced by the application of load to said boom said second shaft is rotated by said pulley.
 13. An overload safety device, as set forth in claim 12, wherein said dynamometer is prestressed to the maximum allowable load.
 14. An overload safety device, as set forth in claim 13, wherein said dynamometer is mounted on the portion of said boom disposed in compression under load conditions.
 15. An overload safety device, as set forth in claim 14, wherein said dynamometer extends in the longitudinal direction of said boom and is mounted on the compression surface of said boom.
 16. An overload safety device, as set forth in claim 10, wherein means are arranged for rotatably biasing said second shaft for displacing said swivel arms laterally outwardly away from said cam discs, and means forming a safety pocket for receiving said combination-photocell assembly for interrupting the passage of light between the light source and the photocells thereof and discontinuing loading operations on said crane.
 17. An overload safety device, as set forth in claim 10, wherein a bulb is positioned on said second shaft and said light sources consist of cable conductors extending from said bulb.
 18. An overload safety device, as set forth in claim 8, wherein said housing encloses said cam discs, said swivel arms and said pendulums, a partition dividing said housing into two compartments, one of said compartments containing said cam discs and swivel arms and the other one of said compartments containing said pendulums, and said partition supporting said first shaft for said cam discs.
 19. An overload safety device, as set forth in claim 9, wherein said setting member having a radially extending circumferential edge spaced axially from the face of said setting member containing said recesses and located morE remotely from said cam discs than the face containing said recesses, a third shaft in axial alignment with said first shaft, an engagement member secured on and axially displaceable along said third shaft and arranged to engage said circumferential edge of said setting member, said drive means secured to said engagement member for axially displacing said engagement member into engagement with the circumferential edge of said setting member for axially displacing said setting member and removing it from engagement with said locking pin. 